It is known in some cellular telephony applications to install and activate a data carrier, such as a Subscriber Identity Module (SIM), in a cellular telephone so as to enable the cellular telephone to operate fully, otherwise a limited service is available. For example, in the Global System for Mobile communication (GSM) system, a SIM must be installed and activated in a GSM telephone in order to be able to use the GSM telephone, otherwise emergency calls may only be placed.
Less common, but still known in the art, is a cellular telephone having the capability of receiving two SIMs (a dual-SIM configuration): a semi-permanently installed SIM or fixed SIM having a first subscription associated therewith, and a visiting SIM having a second subscription associated therewith which may vary depending upon a user of the cellular telephone. The visiting SIM can be installed intermittently when required by the user. In such a configuration, even if both SIMs are electrically coupled to the cellular telephone, only one of the two SIMs is activated, since only one of the first and second subscriptions can be accepted by the network for any single cellular telephone. Therefore, the fixed SIM is usually disregarded or electrically decoupled from the cellular telephone when the visiting SIM is installed, the visiting SIM being activated in preference to the fixed SIM. The fixed SIM is thus not visible to the network.
When the visiting SIM is removed, the fixed SIM is activated and the first subscription becomes the active subscription in the network. If another, or the same visiting SIM is re-installed, the fixed SIM is deactivated and the first subscription not used; the new or the same visiting SIM and associated second or other subscription becomes active. Generally, since the visiting SIM has priority over the fixed SIM, if the visiting SIM is never removed, the fixed SIM is never activated.
Applications are emerging for cellular telephones integrated into vehicles in order to add functionality to security or safety features of the vehicle. However, in order for such security or safety features to be efficient and effective, data stored on the fixed SIM must be accurate and up-to-date.
In the above described dual-SIM configuration, this is not realistically achieved, since it is not possible to guarantee that the fixed SIM can be kept up-to-date because of the possibility that the fixed SIM may never communicate with the network for a prolonged period of time. It is therefore an object of the present invention to provide a data carrier system which obviates or mitigates the above described problem.